The present invention relates to a method and apparatus for monitoring a state of polymeric materials, in which a state of polymeric materials such as plastics, rubber, asphalt, or the like depending on a temperature change is monitored by using propagation characteristics of an ultrasonic wave and, more particularly, to a monitoring method and apparatus for measuring a degree of solidification of an asphalt paved road after completion of a paving construction by using the propagation characteristics of the ultrasonic wave.
Hitherto, in polymeric materials such as a synthetic resin or the like, a discrimination as to whether or not the polymeric materials have reached a solid state due to a decrease in temperature from a viscous liquid state due to a heating process and have been changed to a state having sufficient usable practical strength or not is effected by monitoring a temperature of an object to be measured or the passage of time.
However, in the case of monitoring the temperature, since a temperature distribution in an object to be measured is ordinarily not uniform, the monitoring is executed by merely measuring a local temperature and it is difficult to accurately determine the temperature of the object. On the other hand, in the case of monitoring by the time, there is a problem such that there is a large variation of an object to be measured depending on environmental conditions such as temperature, humidity, and the like, so that the monitoring becomes unstable.
On the other hand, in the case of asphalt pavement, a traffic lane can be opened and restarted in a short time after completion of the paving construction as compared with the case of a cement concrete pavement. However, there is a problem in that if the traffic lane is opened too early, the road surface is deformed after the traffic lane was opened because the asphalt pavement was not yet completely solidified. In addition, if a traffic lane shut-off time is set to a too long time, a problem such as a traffic jam or the like occurs. Therefore, it is necessary to open the traffic lane at a proper timing.
Hitherto, as a method of determining the timing to open the traffic lane of the road which was shut off for construction, a method of determining such timing by measuring the surface temperature of the paved road has been known. That is, since it is known that the surface temperature at which the traffic lane can be opened is set to a temperature within a range from 40.degree. to 50.degree. C., the opening of the traffic is instructed, for instance, when the surface temperature of the road is equal to or lower than 45.degree. C. On the other hand, a method whereby a part of the road surface is mechanically pressurized and permission or inhibition of the opening of the traffic lane is determined by checking an amount of depression of the road surface is also used.
However, the surface temperature and the internal temperature of the paved road differ. Such a temperature difference largely depends on the kind of asphalt used, the kind of crushed stones to be mixed and its mixing amount, and environmental conditions such as outside atmospheric temperature, humidity, cooling method of the road surface, and the like. Therefore, even if the surface temperature has decreased to a predetermined temperature such as 45.degree. C. or lower, there is a case where a deep portion of the road is still held at a high temperature and the asphalt is not sufficiently hardened. There is a fear such that if the permission or inhibition of the opening of the traffic lane is unconditionally decided on the basis of the surface temperature of the paved road, the road surface will be deformed after the traffic was opened. On the other hand, in the case of the method whereby a part of the road surface is mechanically pressurized and such a determination is performed on the basis of an amount of depression, there is a problem such that a damage remains on the road surface after completion of the inspection and it is necessary to repair the road surface.